The present invention relates to carbon black for blending in rubber. More particularly, the invention relates to carbon black which can be suitably blended in rubber for use for the tread of passenger tires which is required to possess both of a high abrasion resistance and a high resilience.
Rubber material for constituting the tread of passenger tires is required to have dynamic properties to suppress the loss of the tire driving energy, such as a high resilience and a low heat build-up. Then, to improve the dynamic properties of the rubber material by blending carbon black in the rubber, it is known to be effective to make use of such a carbon black as having a large particle diameter [that is to say, a small BET specific surface area (N.sub.2 SA)]. However, such carbon black shows a disadvantageous behavior with respect to the reinforcement of rubber, and tends to considerably lower the abrasion resistance of the rubber, which is a most important factor characterizing treads of tires and which should preferably be as high as possible.
In view of the above, conventionally it has been practiced to secure a high abrasion resistance of the tread of passenger tires by blending in the rubber for the tire tread a carbon black of the class having a BET specific surface area of at least 85 m.sup.2 /g and, at the same time, attempt to attain an improvement in or relating to the resilience by selectively using a carbon black characterized by having a broad aggregate size distribution.
However, using one of carbon blacks lying within a particle size range smaller than 85 m.sup.2 /g in terms of the BET specific surface area, although an improvement can be realized in or relating to the resilience, a problem is posed such that the abrasion resistance is considerably lowered, and the rubber incorporating the carbon black can be no longer satisfactory in the light of the characteristics required of the rubber member for the tread of passenger tires.